Existing dimmable LED lamps commonly use Triodes for Alternating Current (TRIACs) for dimming control. A Diode for Alternating Current (DIAC) is used in a TRIAC dimming control circuit to control the on and off cycles of the TRIAC.
However, due to the element characteristics of the DIAC, there is a deviation of about 3V between the breakover voltages of the positive and negative half cycles. As a result, the conduction angles of positive and negative half cycles of a TRIAC signal can be different. In other words, the positive and negative half cycle waveforms of the TRIAC signal are not symmetrical. This may cause variations in the brightness (i.e. flickering) of the LED lamp in a full cycle.